(1) Field of the Invention
The present invention relates to a recording apparatus which is equal to a film camera in terms of imaging effect. More specifically, the present invention relates to a recording apparatus used in the digital cinematography field where 2-3 pulldown video and audio signals are recorded for video production, which is equal in terms of quality to the video production made by a film cinema system. Hereinafter, 2-3 pulldown may also be referred to simply as “pulldown”.
(2) Description of the Related Art
For making a movie using film, a progressive video signal is recorded at 24 frames per second and then this 24P signal is reproduced.
In recent years, digital cinema production which refers to making a movie using a video camera has been suggested as an alternative to film cinema production which refers to making a movie using a film camera. Examples of digital cinema production equipment are explained as follows.
FIG. 1 is a diagram showing a configuration example of a usual video camera. As shown, when using the usual video camera, a progressive video signal or an interlaced video signal is recorded at 60 frames per second onto a video tape. Hereafter, the progressive video signal is referred to as the “60P signal” whereas the interlaced video signal is referred to as the “60I signal”.
FIG. 2 is a diagram showing a configuration example of digital cinema production equipment that employs a pulldown recording method. As shown, when using the digital cinema production equipment employing the pulldown recording method, a captured image is stored as a 24P signal which is first converted into a 60P or 60I signal by a pulldown conversion unit and then is recorded onto a video tape. For reproduction, a reverse pulldown conversion unit of the digital cinema production equipment converts the 60P or 60I signal back into the 24P signal. Or, without such conversion, the 60P or 60I signal is provided for reproduction. By doing so, a signal processing circuit of a conventional video camera can be used as it is, so that quality systems have been able to be provided at low cost.
Moreover, in recent years, recording media having a high affinity for information technology (IT), such as disc media and semiconductor memory media, have been used in addition to tape media. However, as compared with tape media, these media cost more per recording time. For this reason, a recording method for saving recording capacity, that is, a native recording method, has been suggested.
FIG. 3 is a diagram showing a configuration example of digital cinema production equipment that employs the native recording method. As shown, when using the digital cinema production equipment employing the native recording method, an effective-frame extraction unit deletes a redundant video signal from the 60P or 60I signal which has been pulldown-converted on the basis of pulldown sequence information. Thus, only the video signal necessary for the recording, i.e., the effective frame signal, is extracted and recorded, thereby saving recording capacity.
Moreover, not only recording-reproduction apparatuses having a video capture unit, such as a combination camera-recorder-player apparatus, but also recording-reproduction apparatuses used for backup, dubbing, and editing purposes which have no video capture unit have been suggested.
FIG. 4 is a diagram showing a configuration example of digital cinema production equipment which does not have a video capture unit. As shown, for performing a recording operation using the digital cinema production equipment having no video capture unit, an input unit receives a pulldown-converted 60P or 60I signal, and then an effective-frame extraction unit extracts the effective frame signal on the basis of pulldown sequence information detected by a pulldown sequence detection unit.
When the input signal is pulldown-converted in the apparatus as in the cases of the recording-reproduction apparatuses having the video capture units as shown in FIGS. 2 and 3, the pulldown sequence information used for extracting the effective frame signal can be controlled in the apparatus and, in general, the pulldown sequence information is controlled as information repeated every predetermined period of time.
On the other hand, when the input signal is a 60P or 60I signal as in the case of the recording-reproduction apparatus having no video capture unit as shown in FIG. 4, the pulldown sequence information of the input video signal is not always repeated, or continuous, every predetermined period of time. In addition, a usual 60P or 60I signal which has not been pulldown-converted may be received. For such a case, the pulldown sequence detection unit and the effective-frame extraction unit are designed so as to reduce visual discomfort caused by the effective frame signal.
For example, a method for extracting the effective frame signal in the case where the 60I input signal includes both the 2-3 pulldown video signal and the 2-3 non-pulldown video signal has been suggested (refer to Japanese Unexamined Patent Application Publication No. 2007-82040, for example). According to this extracting method, the effective frame signal is extracted as follows on the basis of the pulldown sequence information. When the 60I input signal is the 2-3 non-pulldown video signal, the 60I signal is converted into the 60P signal. When the 60I input signal is the 2-3 non-pulldown video signal, the 60I signal is reversely pulldown-converted into the 24P signal which is then converted to the 60P signal. In this way, the extraction is performed by switching between the signals which are accordingly converted. It should be noted here that in the above-mentioned reference No. 2007-82040, the video signal processing is described and the audio signal processing is not considered.
Using the configuration examples shown in FIGS. 1 to 4, the video signal processing has been described. However, the recording-reproduction apparatus records and reproduces an audio signal as well as the video signal. As a condition for doing this, the video signal and the audio signal received and recorded at the same timing need to be provided for reproduction at the same timing. In other words, the video signal and the audio signal need to be synchronized. This is because when watching a material in which the video signal and the audio signal are out of synchronization, one may experience discomfort or even feel sick. Moreover, the input signal disturbed during recording can end up being material with noise, requiring man-hours to delete the noise part from the material.
FIG. 5 is a diagram showing a method for recording video and audio using the usual video camera. As shown, when using the usual video camera, the input video signal and the input audio signal are recorded without being deleted. Here, it should be noted that descriptions regarding delays caused by the signal processing and the like are omitted in the present and following diagrams explained below.
FIG. 6 is a diagram showing video and audio data of material recorded using the usual video camera. From this diagram, it should be understood that the video signal and the audio signal of this material can be synchronized for reproduction when the reproduction of the recorded video data and the recorded audio data are started at the same timing.
FIG. 7 is a diagram showing a method for recording video and audio using the pulldown recording method. FIG. 8 is a diagram showing the video and audio data recorded using the pulldown recording method. As in the cases shown in FIGS. 5 and 6, the video signal and the audio signal are recorded without being deleted, and it should be thus understood that the video signal and the audio signal of this material can be synchronized for reproduction when the reproduction of the recorded video data and the recorded audio data are started at the same timing. Note that it does not matter if the signal is a 60P signal or a 60I signal.
FIG. 9 is a diagram showing the native recording method for the 60P signal. Video recording command information shown in this diagram is used for control to record or not to record the 60P input signal, in accordance with the pulldown sequence information detected by the pulldown sequence detection unit as shown in FIG. 4. Here, the pulldown sequence detection unit may detect the pulldown sequence information: by comparing the input video signal data; by calculating a numeric value of time code information superimposed on the input video signal; or by referring to the pulldown sequence information allocated to user's bit information superimposed on the input video signal.
As shown in FIG. 9, the pulldown sequence information is represented by a numeric value from 0 to 4, and one set of pulldown sequence information is allocated to two frames of the 60P signal. It should be noted that a frame assigned 0 as the pulldown sequence information is referred to as the “top” of the sequence.
Here, one set of pulldown sequence information is allocated to two frames of the 60P signal as mentioned above, in order to maintain compatibility between the 60P signal and the 60I signal in the case of mutual conversion. The 60I signal constructs one piece of video by one frame, i.e., two fields, and one set of information, such as the time code information and the pulldown sequence information attached to the video, is allocated to two fields. When the 60P signal and the 60I signal are mutually converted, two fields of the 60I signal correspond to two frames of the 60P signal on a time axis. This is why one set of the pulldown sequence information is allocated to two frames of the 60P signal. Note that, out of the two fields of the 60I signal, an anterior field is referred to as the first field whereas a posterior field is referred to as the second field. Also note that, out of the two frames of the 60P signal, an anterior frame is referred to as the first frame whereas a posterior frame is refereed to as the second frame.
The video recording command information is controlled in the following manner. When the pulldown sequence information is 0 or 1, only the first frame is to be recorded. When the pulldown sequence information is 2 or 3, only the second frame is to be recorded. When the pulldown sequence information is 4, neither of the two frames is to be recorded. Through such control over the video signal, only the frames out of the 60P signal indicated to be recorded according to the video recording command information are extracted as the effective-frame signal. This signal is processed as the to-be-recorded video data and is then recorded. Meanwhile, regarding the audio signal, the audio record command information is controlled in such a manner that audio is recorded all the time while the recording operation is being performed. Thus, the audio signal is recorded without being deleted.
FIG. 10 is a diagram showing the video and audio data recorded according to the native recording method. As shown, when the data is recorded according to the native recording method, the recorded video data is reduces as compared with the cases shown in FIGS. 6 and 8. In other words, it can be understood that the recording capacity is saved. Moreover, when the native recording method is employed, the video signal and the audio signal cannot be synchronized simply by starting the reproduction of the recorded video data and the recorded audio data at the same timing. To be more specific, the to-be-recorded video data is shorter, meaning that the reproduction would be completed earlier.
Against this backdrop, there are methods for synchronizing the video signal and the audio signal of the material recorded as shown in FIG. 10. With reference to FIGS. 11 to 14, these methods are explained as follows.
FIG. 11 is a diagram showing a method for reproducing the 60P video through pulldown conversion. As shown, when the recorded video data of the 60P video is to be reproduced according to this method employing the pulldown conversion, the first frame of the recorded video is converted to the first and second frames of the 60P video for reproduction, and the second frame of the recorded video is converted to the third, fourth, and fifth frames of the 60P video for reproduction. By continuing the reproduction in the same manner after this, the video and audio are reproduced in synchronization with each other.
FIG. 12 is a diagram of showing a method for reproducing the 24P video through frame rate conversion. As shown, when the 24P video is to be reproduced according to this method employing the frame rate conversion, a reproduction period of time per frame of the recorded video data is increased so that the video and audio are reproduced in synchronization with each other.
FIG. 13 is a diagram showing a method for reproducing the 60I video through pulldown conversion. As shown, when the recorded video data of the 60I video is to be reproduced according to this method employing the pulldown conversion, the first frame of the recorded video is converted to the first and second fields of the first frame of the 60I video for reproduction, and the second frame of the recorded video is converted to the first and second fields of the second frame and the first field of the third frame of the 60I video for reproduction. Also, the third frame of the recorded video is converted to the second field of the third frame and the first field of the fourth frame of the 60I video for reproduction. Moreover, the fourth frame of the recorded video is converted to the second field of the fourth frame and the first and second fields of the fifth frame of the 60I video for reproduction. By continuing the reproduction in the same manner after this, the video and audio are reproduced in synchronization with each other.
FIG. 14 is a diagram showing a method for reproducing 24PsF video through frame rate conversion. As shown, a 24PsF signal is a video signal of the 24PsF video and is generated by interlacing the 24P signal. According to this method for reproducing the 24PsF video through the frame rate conversion, the video and audio are reproduced in synchronization with each other as in the case shown in FIG. 12.
FIG. 15 is a diagram showing the native recording method for the 60I signal. Video recording command information shown in this diagram is used for control to record or not to record the 60I input signal, in accordance with the pulldown sequence information detected by the pulldown sequence detection unit as shown in FIG. 4. Here, the pulldown sequence detection unit detects the pulldown sequence information using the same way employed in the case of the native recording method for the 60P signal.
As shown in FIG. 15, the pulldown sequence information is represented by a numeric value from 0 to 4, and one set of pulldown sequence information is allocated to one frame, i.e., two fields, of the 60I signal. It should be noted that a frame assigned 0 as the pulldown sequence information is referred to as the “top” of the sequence. The video recording command information is controlled in the following manner. When the pulldown sequence information is 0, 1, or 3, both the first and second fields are to be recorded. When the pulldown sequence information is 2, only the second field is to be recorded. When the pulldown sequence information is 4, only the first field is to be recorded.
The processing of extracting the effective-frame signal is performed as follows. When a recording command is given according to the video recording command information so as to record from the first field, the first and second fields of the currently being received 60I signal are extracted as the effective-frame signal. When a recording command is given according to the video recording command information so as to record from the second field, the second field of the currently being received 60I signal and the first field of a next-to-be received 60I signal are extracted as the effective-frame signal.
Through such control over the video signal, only the fields out of the 60I signal indicated to be recorded according to the video recording command information are extracted as the effective-frame signal. This signal is processed as the to-be-recorded video data and is then recorded. Meanwhile, regarding the audio signal, the audio record command information is controlled in such a manner that audio is recorded all the time while the recording operation is performed. Thus, the audio signal is recorded without being deleted. Accordingly, the recorded data is the same to-be-recorded video and audio data in the case of using the native recording method employed for the 60P signal shown in FIG. 10.
In this way, under the right conditions, such as when the input signal is stable and the input signal is received continuously without being switched, the video signal and the audio signal can be synchronized for reproduction according to the above-described method.
However, when the input signal is received discontinuously, such as when the input signal is disturbed or switched, a time lag occurs between the video signal and the audio signal in the case where the recording capacity is to be saved. For this reason, there is a problem that the video signal and the audio signal cannot be synchronized for reproduction according to the above-described method.
For example, when the input signal is the 60P or 60I signal as described above, the input signal is not always continuous. Also, the 60P or 60I signal which has not been pulldown-converted may be received. Moreover, there may be a possibility that the input signal is disturbed due to the reasons such as when the power of a reproduction-side equipment is turned off and on during a recording operation executed for the purpose of making a copy, when a connection cable is removed and inserted, or when noise occurs to the connection cable.